Understanding Efficiency

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# Understanding Efficiency - PowerPoint PPT Presentation

Understanding Efficiency. Human Circuit. How does it work?. Remember how lie detectors work? People are conductors. Electricity is nothing more than free electrons moving from atom to atom through a material. This flow is called a current .

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## Understanding Efficiency

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Presentation Transcript

### Understanding Efficiency

Human Circuit

How does it work?
• Remember how lie detectors work? People are conductors.
• Electricity is nothing more than free electrons moving from atom to atom through a material. This flow is called a current.
• Since your body is mostly water and there are water and minerals on your skin, your body can be a conductor, but it’s not a great one.
Some motors run on direct current:
• Electricity runs in one directions.
• Mp3 players, computers, cell phones & calculators also use DC.
• Plug-in devices that run on DC come with their own power supplies that convert the power company’s 120-V AC to DC.
The Electricity in household circuits is AC
• “Alternating Current” flows back and forth, 60 times per second.
Why do power companies generate AC?
• With AC they can use transformers.
• Transformers change the amount of voltage with hardly any energy loss.
• Changing voltage is necessary because the most efficient way to transmit current over long distances is at a high voltage.
But…
• When transmission lines carry current at 500 000 V, the voltage must be reduced before it can be used in your home.
Generating Electricity
• Remember our good friend Michael Faraday?
Electromagnetic Induction
• Faraday demonstrated that electrical current could be generated (by moving a conducting wire through a magnetic field).
• This changed the world because it introduced a way to generate a steady supply of large amounts of electricity.
• Generators coils of wire that are moved through a magnetic field.
Tokyo's Toshima Incineration Plant
• Burns 300 tons of garbage a day, turning it into electricity, hot water and a kind of recyclable sand.
The unit of power is:
• The Watt (W) – Named for James Watt
• A watt is equal to one joule per second.
• The faster a device converts energy, the greater its power rating.
Power Ratings:
• Most small appliances: 1500 W or less
• Stove: 7000 W
• Calculator: 0.4 mW
Mathematically:
• Power is equal to the current multiplied by the voltage.
• Power (P); current (I); voltage (V)
Energy: Measured in Joules (watts x seconds)
• You can use the power rating of a device to figure out the amount of energy the device uses.
• Remember that power is the rate at which a device converts energy. You can find the amount of energy by multiplying this rate by the length of time the device operates.
Kilowatt Hours
• People use a lot of joules of energy in their homes/businesses, so kilowatt hours are often used as a unit for energy.
• Calculation is the same, except hours are substituted for seconds, and kilowatts (kW) are substituted for watts.
• Electricity meters measure the energy used in kilowatt hours.
Law of Conservation of Energy
• Energy cannot be created or destroyed.
• It does not just appear or disappear… it must be transformed from one form to another.